1. Field of the Invention
The present invention relates to a magneto-optic disk system, more particularly, to a floating type magneto-optic disk reading head system used in a magneto-optic disk system, having an external semiconductor laser resonator which operates at orthogonal two mode oscillations.
2. Description of the Related Art
JPA 61-134943 discloses a reading head in an optical disk system; the reading head comprises a semiconductor laser. A non-reflective film is provided at an end of the laser facing an optical disk, and a film having a high reflectivity is provided at another end of the laser facing an optical fiber, for detecting read data. When the laser is energized, a laser oscillation, i.e., a resonation, is established between the high reflectivity film and the optical disk. Namely, the optical disk, the laser, and the high reflectivity film cooperate and function as an external resonator. The optical disk is provided with pitted portions wherein data is stored and non-pitted portions where data is not stored. A reflectivity at a pitted portion is lower than that at a non-pitted portion. When a laser light emitted from the laser exposes a pitted portion, a low laser oscillation occurs, and thus little light is received at the optical fiber. Conversely, when the laser light exposes a non-pitted portion, a high laser oscillation occurs, and thus a high amplitude light is received at the optical fiber. The data reproduction of the optical disk system is made by using this difference in the light received for a data read.
Magneto-optic disk systems, which are known as rewritable optical disks and are operated by an optical-magnetical recording method using a Kerr effect, are now in practical use. In the magneto-optic disk systems, an optical modulator or a magnetic field modulation is adopted (NIKKEI BYTE, 1985, March, pp. 94-98, NIKKEI ELECTRONICS, 1988, 2, 8, No. 440, pp. 115-119) and in both modulations, a phase change in a vertical magnetized film of a magneto-optic disk is used for reading and writing data, i.e., the phase change is detected by using the Kerr effect. Namely, in the magneto-optic disk system, the difference of the reflectivity of the optical disk set forth above can not be adopted for reading data, and as a result, the external resonator described above can not be applied to the magneto-optic disk head.
U.S. Pat. No. 4,637,027 based upon Japanese patent application No. 58-177233 (JPA 60-68684) and Japanese patent application No. 58-177227 (JPA 60-69573) discloses a laser light source device having a resonator, and used for a detection of various physical properties, for example, a magnetic field. The external resonator includes a reflection mirror, a first quarter wave (.lambda./4) plate, a semiconductor laser, a second quarter wave plate, a Faraday rotator, and an output mirror such as a half mirror. A first signal having a frequency (f+.DELTA.f) and a second signal having a frequency (f-.DELTA.f) are output from the output mirror, and a frequency of a beat signal obtained by an interaction of the first and second signals is c.phi./.pi.L; where c denotes a speed of a light, .phi. denotes a rotation angle of the Faraday rotator, and L denotes an effective cavity length of the external resonator. This frequency, however, is low, and thus detection of the frequency is difficult. Further, the reflection mirror forming a part of the resonator is only a mirror.
A prior art reading head for a magneto-optic disk system is very complex and heavy, and as a result, a high speed access cannot be obtained.
Ukita, et al., proposes a floating type reading head used in an optical disk system ("Read out Characteristic of Micro Optical Head Operated in Bi-Stable Mode", ISOM '87). This reading head uses a change of the reflectivity discussed above, and thus cannot be used for a magneto-optic disk reading head. Accordingly, a compact and light weight reading head for a magnetic-optic disk system is still required.